For a paper feed roller used for paper feeding in image forming apparatus such as an electrostatic copying machine and various kinds of printers, one with a roller body formed of elastic material such as crosslinked rubber in a cylindrical shape and whose peripheral surface is a contact surface to paper is generally used.
Paper powder generated from paper and dirt tend to be adhered to a peripheral surface of a paper feed roller, and an accumulation of paper powder and dirt on the peripheral surface of the roller after repetition of contacts with paper may decrease the friction coefficient of the peripheral surface of the roller to paper and cause defective paper carrying relatively early. Therefore, various kinds of surface forms has been studied and put in use (see, for example, JP2014-34428A).
JP2014-34428A, for example, discloses a paper feeding roller of elastic material in which a plurality of protruding lines are disposed at even intervals on its surface. The cross section of the protruding lines disclosed in JP2014-34428A, cut orthogonal to an axial direction of a roller body, is substantially shaped in a right angled triangle having the front side of a rotational direction of the roller body in a circumferential direction of the roller body as the hypotenuse and the back side as the adjacent side corresponding to a straight line extending through a central axis of the roller body. Also, these protruding lines are formed so that the crossing point of the hypotenuse and the adjacent side has a rounded shape. Also, JP2014-34428A discloses that an opening angle of the protruding lines, being an angle between adjacent protruding lines about the central axis of the roller body, is equal to or more than 2° and is equal to or less than 8° and a height of the protruding lines in a radial direction is equal to or more than 0.1 mm and is equal to or less than 0.5 mm. With the protruding lines having a height equal to or more than 0.1 mm contact pressure to paper is increased and defective paper carrying is inhibited.